At present, building blocks are widely used in a variety of circuit designs and production. Building blocks include power switches, inductors and capacitors. In order to increase the power density and switching frequency, it is necessary to design highly integrated building blocks.
FIG. 1 shows a schematic of DC-DC converter. SW1 and SW2 are two MOS switches. In this circuit, using CMOS technology, SW1 and SW2 could be integrated in a building block. The existing integrated MOS structure is shown in FIG. 2, in which two MOS units with contrary polarity are located on the p-substrate and n-well, respectively. The source and drain electrodes of SW1 and SW2 are both on the surface. The drain electrode of SW1 and the source electrode of SW2 are connected to the Vin and GND respectively. The drain electrode of SW2 and the source electrode of SW1 are connected and provide the voltage potential VX, which is controlled by the switching of SW1 and SW2.
Such structure has the following problems: 1) Because of the side-current, the lateral structure is subject to the self-bias-effect in the P-substrate and the N-well. Therefore, the die size and the output current of the converter are limited. 2) Its breakdown voltage is lower than that of the discrete structure. 3) The power density and the die size are also limited by the current electrode (Vin, GND, VX) and the surface of the chip.